When sheet metal or metal plate is formed on a press brake, the behavior of the material and the resulting bend profile are dependent on two key variables: the geometry of a tool or tooling used, and the strength and composition properties of the material being formed. This creates an almost infinite number of possible outcomes with respect to how the material will behave during bending. This possibility results in a frustrating and costly process every time a new material or tool combination is used.
Various methods are used to try to address this problem. There exist published tables of bend parameters that are based on a particular material's statistical strength properties, i.e., a bend allowance or K-factor table. One of these parameters together with a specified inside bend radius can be used to manually calculate how the part will behave, or may be employed in a CAD/CAM or 3D design and unfolding software system to “unfold” the part for purposes of planning the location of the desired part features, e.g., folds, bends, and the like. However, utilizing or creating K-factor tables involves an iterative process of trial bending and measurement that relies on the expertise and experience of the operator.
A blank for a part is cut, for example using a CNC plasma machine, a turret punch, laser, or other cutting or forming device. A test part is formed and measured. Depending on how close the selected bend parameter and radius is to the actual material, the finished part can be close to the correct size, or can be significantly larger or smaller than required. If the part is not close to the desired size, one or various parameters may need to be adjusted since there is more than one parameter that can be adjusted to reduce or eliminate the error. One may rely upon adjustment of two factors to control or adjust the finished form size of a part, i.e., the inside radius and either the bend allowance or the K-factor. The inside radius, the bend allowance, and the K-factor are related.
During adjustment of these parameters, the inside radius value is often manipulated to a less than accurate value simply because the inside radius is the easiest parameter to adjust. While such a parameter change does adjust the formed size of a part, the over-manipulation of the inside radius value can create additional problems. For example, while the finished part may be closer to the desired size, the inside radius used by the design system has been adjusted to an inaccurate value with respect to any mating parts. As such, the finished part may be formed within tolerance, but the mating parts will have to be adjusted to match the profile of the formed part—a step that further complicates the job of part design.
As such, in many manufacturing operations it takes several attempts to get a part correct. Even more attempts may be required to get a correct set of mating parts. This can result in significant hard costs lost to scrapped test material, lost machine time in cutting test parts, and labor costs since this process often involves two or more people. The end result of all of these difficulties is that prototype development can be the most costly part of production as prototype development generates no revenue, and must be done to provide a proof of performance capability in the contract manufacturing market and OEM's.